Browsers and plugins

What is it with browser plugins that make them destroy an otherwise useful system? Example, on my notebook, with XP and Firefox, I can’t make use of the Acrobat PDF viewer. It takes about 3 minutes to load a PDF (no matter what size), renders my browser unusable during that time, and usually crashes the browser totally afterwards. Next is my AMD64 Gentoo system using Mozilla and mplayerplug-in. If I view a WMV file I don’t have the codec for (normally WMV10), it will sometimes play the audio without video, and totally segfault the browser when I close that window, or press back. In my book, a plugin shouldn’t crash the entire browser session. Just a worthless design I guess.